1. Field of the Invention
The present invention relates to a golf club head, more particularly to a joint structure of a metal member made of a metal material and a FRP member made of a fiber reinforced resin.
2. Description of the Related Art
The laid open Japanese patent application JP-P2003-250933A discloses a hollow golf club head “a” composed of a metal member b made of a metal material and a FRP member c made of a fiber reinforced resin, as shown in FIG. 15. The metal member b has an opening d, and the FRP member c is attached to the metal member b and covers the opening d. This head “a” can save the weight thereof on the basis of the small specific gravity of the resin. Further, the saved weight can be allocated, for example, in the sole portion or the like, and can improve degree of freedom in the weight allocation design or the like.
The FRP member c is generally made of a plurality of prepreg plies e, as shown in FIGS. 16(A) to 16(C). FIGS. 16(A) and 16(B) each is a plan view showing an example of unidirectional prepreg ply e1 (which are called also as “UD prepreg” in the industry). The ply e1 comprises reinforcing fibers “f” aligned along unidirection in a matrix resin R thereof. FIG. 16(C) is a plan view showing a cloth prepreg ply e2. The ply e2 comprises a woven fabric having fibers extending in two directions and intersecting each other, in a matrix resin R. Further, the FRP member c is made by laminating a plurality of prepreg plies e which are previously preformed in a predetermined shape, and curing in a predetermined shape under heat and pressure.
In the conventional FRP member c, a 0° direction prepreg ply e1a having a fiber orientation of 0 degree with respect to the head longitudinal direction BL, as shown in FIG. 16(A), and a 90° direction prepreg ply e1b having a fiber orientation of 90 degrees with respect to the head longitudinal direction BL, as shown in FIG. 16(B) are used in a state in which the same number of them (for example, two) are laminated. In a laminated structure of the plies mentioned above, a strength can be secured by arranging the directions of the fibers f in the head longitudinal direction corresponding to a direction in which an impact force is directly applied at a time of striking a ball, and a direction perpendicular thereto. Further, there is a case that one cloth prepreg ply e2 is further attached to an outer side.
However, in the conventional FRP member c, a deformation at a time of striking the ball is larger in comparison with the metal material, and an energy loss is larger. Accordingly, a kinetic energy of the head is not efficiently transmitted to the ball. Therefore, in order to improve a carry, it is necessary to further improve the FRP member c.